Are sunscreen hazardous for our skin ???

       

         In sunny summer days use of sunscreen is common for protection from UV rays of sun. From many years nanoparticles are used in sunscreens. Excess use sunscreen raises some health related issues in past few years too. Largest number of case of skin cancer (Melanoma and Non-melanoma) reported in Australia.    

      How sunscreen works on our skin, what is the role of nanoparticles in sunscreen, are really they hazardous for our skin?  What our scientific research reports explain let’s discuss.

How sunscreen works on our skin

       Two type ingredients are used in sunscreens. First one is chemical absorbent which absorb UV rays and protect the skin, but it can be allergic.  Second one is nano size physical blocker as Zinc oxide and Titanium dioxide. They are more effective as compare to absorbent and have no any adverse effect on skin.

Nanoparticles

      Nanoparticles are too small in size their dimension in range of 1-100nm (one nanometer is one billionth part of the meter). Depending of dimensions nanoparticle categorizes as zero-dimension eg. Cluster, one-dimension (1D) eg.  Nanotube, two-dimension (2D) eg. Film, three-dimension (3D) eg. Polycrystal.  Smaller in size and higher in surface area to volume ratio, nano particle shows better chemical and physical properties than their bulkier one. Nanopaticles have several potential applications in field of medicine, biomedical, drug delivery, electronics, optics and as catalyst.

      Health related concern arise because of skin cell penetration power of nanoparticles and still unknown of the effect of their interaction with internal biological systems.

Are nanopaticles hazardous for skin?

    Therapeutic Goods Administration (TGA) is an Australian Government body which regulate all issues related to sunscreen ingredients and their formula. In 2013 TGA conducted a review of all scientific reports, article related to use and effect of nanoparticle in sunscreen. Their report suggest that Zinc oxide and Titanium dioxide do not reach to the viable cells of skin, rather stay on the upper surface of the skin which is not composed of viable cells.

     

        Some more survey has been done recently in Australia. In 2014 the Cancer Council of Australia study and reported that human immune cells (macrophages) when exposed in Zinc oxide nanoparticle; macrophages  absorbed nanoparticles and broken down them. So these nanoparticles did not reach in human blood. If in any case they reached in the blood our immune system make them ineffective. So it can conclude that presence of nanoparticles in sunscreen does not create any health risk in human. Their regular use is safe.

    

      These nanoparticles tend to aggregate and form agglomerates. Agglomerates are bundle of nanoparticles. These agglomerates are big in size but they remain their nanoparticle properties. These agglomerates can break easily but require some energy which would not come from normal use of sunscreens.  Some laboratory tested their own sunscreen which initially contains nanoparticles but they aggregate due to agglomeration.

Manufacturers view:

      Manufacturers suggest that agglomerates above 100 nm not call nanoparticle while other aruge on that and suggest while they aggregates but they retain their identity and nanoparticle properties. Some manufacturers use coating agents to avoid the agglomeration because coated naoparticles cannot agglomerates.  Coated nanoparticles are less reactive than non-coated nanoparticle, so it they could not penetrated the skin and damage the skin.

Scientific view:

     According to scientific view nanoparticle can penetrate the outer dead layer of skin while they cannot damage the inner layer of skin. Another Australian study report that no any damage have been occur when nanoparticles mechanically penetrated (by broken skin cause by acne, wound etc) inside inner layer of skin. It was still unclear that penetrated zinc oxide is actually nanoparticle or Zn ion which had dissolved. As we know Zn ion is essential content of human body and cannot harm. It is possible that if nanoparticle penetrates inner layer of skin, due to their insufficient amount not show any adverse impact on human body.Study of TGA and cancer council of Australia also show that presence of nanoparticle in sunscreen does not show any adverse effect on skin. While still not very clear idea about any adverse effect of nanoparticle Australian “Nano-suncreen” brand has decides to change their sunscreen formulation to make them nano free.

     

       It is an interesting topic of further research for scientists. Further research is required on What is the effect of nanoparticle on dermal adsorption at different natural conditions?, effect of their size on it, what is the exposure time limit etc. At present CSIRO and Macquarie University of Australia are intensely involved in this program. Until any clear result come out, regulatory authorities should required making it mandatory for manufacturer to show warning disclosure on packet of product. Special disclosure should be for use over cuts, acne and mainly for children.

NANOMATERIALS

Nanomaterials are those which have structured components with at least one dimension less than 100 nm. Materials that have one dimension in the nanoscale (and are extended in the other two dimensions) are layers, such as a thin films or surface coatings. Some of the features of computer chips come in this category. Materials, that are nanoscale in two dimensions (and extended in one dimension) include nanowires and nanotubes. Materials that are nanoscale in three dimensions are particles, for example, precipitates, colloids and quantum dots (tiny particles of semiconductor materials). Nanocrystalline materials, made up of nanometre-sized grains, also fall into this category. Some of these materials have been available for some time; others are genuinely new.

Two principal factors cause the properties of nanomaterials to differ significantly from other materials: increased relative surface area, and quantum effects. These factors can change or enhance properties such as reactivity, strength and electrical characteristics. As a particle decreases in size, a greater proportion of atom are found at the surface compared to those inside. For example, a particle of size 30 nm has 5% of its atoms on its surface, at 10 nm 20% of its atoms, and at 3 nm 50% of its atoms. Thus nanoparticles have a much greater surface area per unit mass compared with larger particles. As growth and catalytic chemical reactions occur at surfaces, this means that a given mass of material in nanoparticulate form will be much more reactive than the same mass of material made up of larger particles. 

Significance of the Nanoscale

A nanometer (nm) is one thousand millionth of a meter. For comparison, a red blood cell is approximately 7,000 nm wide and a water molecule is almost 0.3nm across. People are interested in the nanoscale [which we define to be from 100nm down to the size of atoms (approximately 0.2nm)] because it is at this scale that the properties of materials can be very different from those at a larger scale. We define nanoscience as the study of phenomena and manipulation of materials at atomic, molecular and macromolecular scales, where properties differ significantly from those at a larger scale; and nanotechnologies as the design, characterization, production and application of structures, devices and systems by controlling shape and size at the nanometer scale. In some senses, nanoscience and nanotechnologies are not new. Chemists have been making polymers, which are large molecules made up of nanoscale subunits, for many decades and nanotechnologies have been used to create the tiny features on computer chips for the past 20 years. However, advances in the tools that now allow atoms and molecules to be examined and probed with great precision have enabled the expansion and development of nanoscience and nanotechnologies.

The bulk properties of materials often change dramatically with nano ingredients. Composites made from particles of nano-size ceramics or metals smaller than 100 nanometers can suddenly become much stronger than predicted by existing materials-science models. For example, metals with a so-called grain size of around 10 nanometers are as much as seven times harder and tougher than their ordinary counterparts with grain sizes in the hundreds of nanometers. The causes of these drastic changes stem from the weird world of quantum physics. The bulk properties of any material are merely the average of all the quantum forces affecting all the atoms. As you make things smaller and smaller, you eventually reach a point where the averaging no longer works.

            Type of nanomaterials on basis of Dimension

The properties of materials can be different at the nanoscale for two main reasons: First, nanomaterials have a relatively larger surface area when compared to the same mass of material produced in a larger form. This can make materials more chemically reactive (in some cases materials that are inert in their larger form are reactive when produced in their nanoscale form), and affect their strength or electrical properties. Second, quantum effects can begin to dominate the behaviour of matter at the nanoscale - particularly at the lower end - affecting the optical, electrical and magnetic behaviour of materials. Materials can be produced that are nanoscale in one dimension (for example, very thin surface coatings), in two dimensions (for example, nanowires and nanotubes) or in all three dimensions (for example, nanoparticles).

Nanoscale in one dimension

Thin films, layers and surfaces 

One-dimensional nanomaterials, such as thin films and engineered surfaces, have been developed and used for decades in fields such as electronic device manufacture, chemistry and engineering. In the silicon integrated-circuit industry, for example, many devices rely on thin films for their operation, and control of film thicknesses approaching the atomic level is routine. Monolayers (layers that are one atom or molecule deep) are also routinely made and used in chemistry. Engineered surfaces with tailored properties such as large surface area or specific reactivity are used routinely in a range of applications such as in fuel cells and catalysts. The large surface area provided by nanoparticles, together with their ability to self assemble on a support surface, could be of use in all of these applications.

Nanoscale in two dimensions

Two dimensional nanomaterials such as tubes and wires have generated considerable interest among the scientific community in recent years. In particular, their novel electrical and mechanical properties are the subject of intense research.

a) Carbon nanotubes

Carbon nanotubes (CNTs) are typically a few nanometres in diameter and several micrometres to centimetres long (Fig.2). CNTs have assumed an important role in the context of nanomaterials, because of their novel chemical and physical properties.

Fig. 2

They are mechanically very strong, flexible, and can conduct electricity extremely well. All of these remarkable properties give CNTs a range of potential applications: for example, in reinforced composites, sensors, nanoelectronics and display devices.

b) Inorganic nanotubes

Inorganic nanotubes and inorganic fullerene-like materials based on layered compounds have excellent lubricating properties, resistance to shockwave

c) Nanowires

Nanowires are ultrafine wires or linear arrays of dots, formed by self-assembly. They can be made from a wide range of materials. Semiconductor nanowires made of silicon (Fig 3), gallium nitride and indium phosphides have demonstrated remarkable optical, electronic and magnetic characteristics.

                         Fig 3 Silicon nanowire                             

Nanowires have potential applications in high-density data storage; either as magnetic read heads or as patterned storage media.

d) Biopolymers

The variability and site recognition of biopolymers, such as DNA molecules, offer a wide range of opportunities for the self-organization of wire nanostructures into much more complex patterns eg. Biocompatible sensors and small, simple motors. Such self-assembly of organic backbone nanostructures is often controlled by weak interactions, such as hydrogen bonds, hydrophobic, or van der Waals interactions. The combination of one-dimensional nanostructures consisting of biopolymers and inorganic compounds opens up a number of scientific and technological opportunities.

Nanoscale in three dimensions

a) Nanoparticles

Nanoparticles are often defined as particles of less than 100nm in diameter. Nanoparticles are of interest because of the new properties (such as chemical reactivity and optical behaviour) that they exhibit, compared with larger particles of the same materials. For example, titanium dioxide (Fig. 4) and zinc oxide become transparent at the nanoscale, however are able to absorb and reflect UV light, and have found application in sunscreens.

Fig. 4 Titanium oxides

Nanoparticles have a range of potential applications: in the short-term in new cosmetics, textiles and paints; in the longer term, in methods of targeted drug delivery where they could be to used deliver drugs to a specific site in the body. Nanoparticles can also be arranged into layers on surfaces, providing a large surface area and hence enhanced activity, relevant to a range of potential applications such as catalysts.

b) Fullerenes (carbon 60)

C60 are spherical molecules about 1nm in diameter, comprising 60 carbon atoms arranged as 20 hexagons and 12 pentagons: the configuration of a football (Fig 5).



Fig 5 Buckminster Fullerene C60

Several applications are envisaged for fullerenes, such as miniature ‘ball bearings’ to lubricate surfaces, drug delivery machines and in electronic circuits.

c) Dendrimers

Fig. 6

Dendrimers (Fig 6) are spherical polymeric molecules, formed through a nanoscale hierarchical self-assembly process. They are used in conventional applications such as coatings and inks; they can act as nanoscale carrier molecules and as such could be used in drug delivery. Environmental clean-up could be assisted by dendrimers as they can trap metal ions, which could then be filtered out of water with ultra-filtration techniques.

d) Quantum dots

If semiconductor particles are made small enough (Fig. 7), quantum effects come into play, which limit the energies at which electrons and holes (the absence of an electron) can exist in the particles. As energy is related to wavelength (or colour), this means that the optical properties of the particle can be finely tuned depending on its size.

Fig. 7

Thus, particles can be made to emit or absorb specific wavelengths (colours) of light, merely by controlling their size. Recently, quantum dots have found applications in composites, solar cells and fluorescent biological labels (for example to trace a biological molecule) which use both the small particle size and tuneable energy levels. Recent advances in chemistry have resulted in the preparation of monolayer-protected, high-quality, monodispersed, crystalline quantum dots as small as 2 nm in diameter, which can be conveniently treated and processed as a typical chemical reagent.